Various honeycomb structures made of foldable material are disclosed in the prior art. For example, U.S. Pat. Nos. 4,450,027; 4,603,072 and 4,631,108 to Colson disclose a honeycomb structure constructed by folding a continuous length of foldable material at diametrically opposite sides partially over itself into a tubular form as an individual cell. In addition, U.S. Pat. No. 4,677,012 to Anderson discloses a honeycomb structure formed of a continuous length of foldable material having its longitudinal edges folded over one side of the material and secured to a separate strip material. In this patent the cells are also formed one by one and an additional strip material is required. Another U.S. Pat. No. 4,631,217 to Anderson discloses a honeycomb structure formed of a continuous length of foldable material which is folded into a Z-configuration. In this patent each cell is constituted at front face by a piece of material and at rear face by another piece of material, in which each piece of material is extended from one cell to adjacent cell. Anyway, individual cell is formed by each one half of two pieces of material.
The inventor of the present application found that these honeycomb structures disclosed in afore-mentioned prior art can be manufactured only at a lower productivity since the production rate cannot be speedup due to the unit cell is made individually, and thus the quality of the products is relatively not easy to control uniformly.